Everyone should get vitamin B12 and vitamin D tests on their routine medical blood tests, particularly if you have diabetes or have risk factors for diabetes. A recent study from China found that vitamin D deficiency (hydroxyvitamin D less than 20 ng/mL) is common in diabetics, and that diabetics who lack vitamin D are at markedly increased risk for nerve damage when compared to diabetics who are not vitamin D deficient (Diabetes Res Clin Pract, March 2024:209:111585). Many previous articles found an association between lack of vitamin D and nerve damage in diabetics (Diabetes Metab Res Rev, 2023 Oct;39(7):e3679;Â Cureus, 2021 Jan 5;13(1):e12506).
Lack of B12 is also associated with diabetic nerve damage, and the greater the B12 deficiency, the more frequent the nerve damage. Higher doses of metformin to treat diabetes were associated with increased risk for B12 deficiency and nerve damage (Endocrine Selections of Eur Soc of Endocrinology, Oct 2019;8(10):1324-1329).
Many Diabetics Do Not Know They Have Diabetes
Diabetes and pre-diabetes are very common in North America. More than 40 million North American adults have diabetes and 100 million have pre-diabetes, so nearly one out of every two adults will suffer from the harmful side effects of diabetes. Both diabetes and pre-diabetes put a person at high risk for nerve damage called peripheral neuropathy, and lack of vitamin B12 or D both markedly increase that nerve-damage risk.
A normal fasting blood sugar (less than 100 mg/dL) does not rule out diabetes. Up to 30 percent of diabetics do not know that they are diabetic because they are told that they have normal fasting blood sugar levels. A high blood sugar after meals (more than 100) is often called pre-diabetes and it also increases risk for heart attacks, strokes and all the other effects of diabetes, even if the conventional fasting blood sugar test is normal (Diabetes Metab, 2022; 48101395).
The treatment for diabetes may increase risk for B12 deficiency, because part of the recommended treatment is a plant-based diet, which is likely to be low in vitamin B12 (B12 is found only in foods from animals such as meat, fish and poultry). So all pre-diabetics and diabetics are at significantly-increased risk for the nerve damage caused by diabetes itself and the recommended treatment of diabetes is to markedly increase intake of lots of unrefined vegetables, whole un-ground grains, beans, seeds and nuts, none of which contain vitamin B12.
Vitamin D Deficiency Increases Nerve Damage in Diabetics
Virtually all the harmful side effects of diabetes are associated with inflammation, an overactive immune system that attacks and destroys a person’s own cells in the same way that it attacks and destroys germs that try to invade the bloodstream. Vitamin D helps to dampen down inflammation and protect your cells from being destroyed by an overactive immune system. Lack of vitamin D increases insulin resistance, so a person does not respond to insulin and blood sugar levels rise higher to damage every cell in the body. Higher vitamin D levels are associated with reduced insulin resistance and lower blood sugar levels in diabetics (Diabetol Metab Synd, 2013;5:8).
Risk Factors for Diabetes
• overweight
• age over 65
• physically inactive
• sit for long periods of time
• had diabetes during pregnancy
• gave birth to a baby weighing nine pounds or more
• a large waist circumference (male-greater than 40 inches, female-greater than 35 inches)
• can pinch more than 2.5 inches of skin and fat next to your belly button
• have blood pressure greater than 135/90
• have LDL (bad) cholesterol greater than 100 mg/dL
• have HDL (good) cholesterol lower than 40 mg/dL
• HbA1c greater than 5.7 percent (38.8 mmol/mol) (HbA1c is a blood test that measures sugar stuck on the outer membranes of red blood cells)
• smoke or live with a smoker
• take alcohol regularly
• not getting 7-9 hours of sleep regularly
• have high triglycerides (greater than 150 mg/dL)
• have polycystic ovary syndrome
• have psychiatric disorders (such as schizophrenia, depression, bipolar disorder)
• have obstructive sleep apnea
My Recommendations
Low levels of vitamins B12 and D are so common that I think everyone should get blood tests for vitamins B12 and D at their regular physical examination. This is particularly important if you have any of the risk factors for diabetes, even if you have not been diagnosed as a diabetic or pre-diabetic. Low blood levels of vitamins D and B12 increase risk for serious nerve damage. These deficiencies can be easily remedied with supplements; check with your doctor.
Dr. Gabe Mirkin is a Villager. Learn more at www.drmirkin.com
